Because of their continued rise in growth and development, the specification requirements for batteries used in portable electronic devices has increasingly become more rigid. In particular, batteries having a smaller and thinner size, a high capacity and an excellent cycle characteristic, and a stable performance are in demand. In the field of secondary batteries, the lithium non-aqueous electrolyte secondary battery has spawned a lot of interest because it has a higher energy density than other types of batteries, such that its market share in the secondary battery market continues to grow.
The lithium non-aqueous electrolyte secondary battery comprises a negative electrode, which is a strip of negative electrode collector (current collector), such as copper foil, with both surfaces thereof coated with a negative electrode active material mixture; an positive electrode, which is a strip of positive electrode collector, such as aluminum foil, with both surfaces coated with an positive electrode active material mixture; and a separator, such as micro-porous polypropylene film or the like, interposed between the electrodes. The negative electrode and positive electrode are coiled, each insulated from the other by the separator to form a cylinder or an elliptical cylinder, and if the coiled electrode assembly is for a square-shaped battery, it is pressed flat. The negative electrode and positive electrode are then connected at a predetermined part of the electrode, to a negative electrode or positive electrode terminal lead, respectively, and finally, the assembly is housed in a container of a predetermined shape.
In the manufacture of the coiled electrode assembly, the negative electrode and positive electrode are provided by slitting a negative electrode sheet and an positive electrode sheet, respectively, and thereafter coil around a mandrill. However, the cutting of the negative electrode and positive electrode sheets causes burrs to form at the cut ends thereof, that is, the cut ends of the negative electrode collector and the positive electrode collector made of metal, such that when the coiled electrode assembly is pressed flat, the burrs penetrate the separator to electrically couple the negative electrode and positive electrode, producing a short circuit. This short circuit generates an abnormal amount of heat during use of the battery, lowering the capacity thereof, thereby shortening its service life.
Hence, Japanese laid-open Patent Application No.10-241737, paragraphs 18 to 27, paragraphs 40 to 50, FIG. 1, FIG. 5, and FIG. 7, thereof (Related Art Document 1), and Japanese laid-open Patent Application No.2002-42881, right column of page 3 through left column of page 4, and FIG. 8, thereof (Related Art Document 2), for example, disclose non-aqueous electrolyte secondary batteries that determine the position of the negative electrode when the coiled electrode assembly is formed by multilayer-winding of the positive electrode and the negative electrode with a separator interposed there between, and a predetermined insulating tape, whose thickness is greater than the length of burrs on the positive electrode and/or negative electrode that may cause a short circuit with the electrodes when the coiled electrode assembly is formed, and is attached to at least one surface of the negative electrode whose position has been determined, where a short circuit with the positive electrode may occur, wherein the negative electrode is opposed at least to the positive electrode terminal lead. The non-aqueous electrolyte secondary battery electrode and the manufacturing method thereof disclosed in Related Art Document 1 are explained hereinafter with reference to FIG. 8.
FIG. 8 shows the construction of a coiled electrode assembly of the non-aqueous electrolyte secondary battery disclosed in Related Art Document 1. A mandrill 70 holds the folded ends of two separators 72 and 74, which are strips of insulating sheet. An positive electrode collector 76 has an positive electrode active material mixture layer 78 formed on both surfaces of the middle part thereof, and is exposed on both surfaces near the end CT, to which the positive electrode active material mixture layer is not applied. An positive electrode terminal lead 80 is coupled to the exposed part of the positive electrode collector 76. A negative electrode collector 82 has a negative electrode active material mixture layer 84 formed on both surfaces of the middle part thereof, and is exposed on both surfaces near the end CT, to which the negative electrode active material mixture is not applied.
The positive electrode collector 76 is coiled between the mandrill 70 and the separator 72, and the negative electrode collector 82 is coiled while interposed between the two separators 72 and 74. The positive electrode terminal lead 80 is coupled to the surface, facing the mandrill 70 of the positive electrode collector 76 that is opposed to the end CT of the negative electrode collector 82 through the separator 72. That is, part of the positive electrode collector 76 (to which the positive electrode terminal lead 80 is coupled), is opposed to the end CT of the negative electrode collector 82 through the separator 72.
In the above-mentioned construction, any of the following measures may be adopted to prevent a short circuit from occurring between the positive electrode collector 76 and the negative electrode collector 82:
(1) To cover with an insulating material 88, a part of the surface of the positive electrode collector 76 (to which the positive electrode terminal lead 80 is coupled), which is opposed to the end CT of the negative electrode collector 86 through the separator 72.
(2) To cover with an insulating material 92, either surface facing the positive electrode collector 90 or the negative electrode collector 86 of the separator 72 that exists between a part of the positive electrode collector 76, to which the positive electrode terminal lead 80 is connected, and a part of the negative electrode collector 86 which opposes the above-mentioned part of the positive electrode collector 76 and is near the end CT.
(3) To cover with an insulating material 94, a part of the surface of the negative electrode collector 86 that is near the end CT and is opposed to a part of positive electrode collector 76 where the positive electrode terminal lead 80 is coupled, through the separator 72.
In this case, it is sufficient to provide one of the above-mentioned measures. That is, covering the positive electrode collector 76 with insulating material 88 prevents the burrs on the positive electrode terminal lead 80 from damaging the separator 72, while covering the negative electrode collector 82 with insulating material 94 also prevents the burrs on the positive electrode terminal lead 80 from causing a short circuit even if the burrs penetrate the separator 72. Further, covering either surface of the separator 72 with insulating material 92 also produces the same effects as above-mentioned. The application of insulating material 88, 92, or 94 either by means of a resin coating or an insulating adhesive tape will produce the above-described effects. The use of an adhesive insulating tape however is preferred.